For most modern humans, putting on clothes is second nature. But a new study suggests that our ancestors didn't pick up the habit until relatively recently. The evidence, based on a genetic study of lice, suggests that humans only started dressing when they left Africa for chilly northern climes about 70,000 years ago. Anthropologists reject the surprising conclusion and stand by previous evidence that hominids wrapped up in fur much earlier.

Clues to the start of human clothing are indirect because clothing degrades quickly. Carbon dating of tools for scraping hides has hinted that Neandertals and other hominids that left Africa long before modern humans did got bundled up for northern ice ages as many as 300,000 years ago. Taking a markedly different approach, molecular anthropologist Mark Stoneking of the Max Planck Institute for Evolutionary Anthropology in Dresden, Germany, and colleagues examined head and body lice, which are distinct species. Head lice live on and nibble the scalp, but body lice cozy up in clothing while munching on skin. Because parasites tend to evolve to keep pace with their hosts, the researchers reasoned that the point when head lice migrated to clothing and became body lice would indicate when humans first donned garments.

Stoneking's team used a molecular clock to time how long ago the lice species separated. They sequenced the DNA of 40 strains of head and body lice and counted the differences in the sequences. The team reports in the 17 August issue of Current Biology that head and body lice grew apart about 70,000 years ago, give or take 40,000 years. That suggests modern humans, not Neandertals, invented clothing (unless of course Neandertals' lice went extinct with them), Stoneking says. "Clothing might have been one of the inventions that let [modern] humans be successful."

But if Neanderthals didn't have clothing, they would have needed an extra 67 kilograms of body fat to weather an ice age--weight that would show up on bone studies, says paleoanthropologist Ian Tattersall of the American Museum of Natural History in New York City. Calling the results "absurd," anthropologist Erik Trinkaus of Washington University in St. Louis, Missouri, says that the authors fail to reconcile molecular clock data with contradictory anthropological and archaeological data. "If I may make a bad pun," Trinkaus quips, "it's a lousy article."